THIS WORK compares nano-structured rice husk ash (RHA) before grinding and nano-sized RHA after grinding in terms of the physical properties of cement and mortar performance. Blaine surface area, sieve analysis (45 μm mesh), water of consistency, expansion, initial and final setting time, and compressive strength (at 2, 7, 28, 60 and 90 d of curing) measurements were performed for 0, 2, 4, 6, 8 and 10% RHA replacement of cement by weight. RHA both before and after grinding enhanced the cement physical and mechanical properties, as well as the mortar performance in terms of the long-term aged strength, at a constant water/cement ratio and without the use of any type of super-plasticizer (SP). The enhancement became stable at all long-term ages for 10% replacement in the case of RHA before grinding and 4% replacement in the case of RHA after grinding. More considerable enhancements were observed with a high replacement percentage up to 10% nano-sized RHA due to the small size of its particles, which increased the pozzolanic reactivity and worked as a filler material to produce a denser mortar.